Owing to the wide variety of possible uses of the abovementioned transition metal complexes as catalysts in organic synthesis and, in particular, in the polymerization of olefins, the efficient industrial preparability of sandwich complexes which are disubstituted on the cyclopentadienyl radicals has become increasingly important (EP-A-O 128 045, EP-A-O 366 290, EP-A-O 283 739, EP-O 582 480, U.S. Pat. No. 4,874,880).
The preparation of such compounds is known in principle. The procedure according to equation (1) can generally be used for this purpose, ##STR1## where M can be Li, MgCl or MgBr;
R and R.sup.1 are identical or different and each is an alkyl or aryl radical. PA1 M' is a metallating agent; PA1 M.sup.1 is a transition metal; PA1 X is Cl, Br or I; PA1 m is the oxidation state of M.sup.1 ; and PA1 n.ltoreq.m. PA1 C.sub.1 -C.sub.20 substituted and unsubstituted, alkyl, alkenyl, cycloalkyl, aryl and arylalkyl radicals; PA1 X is Cl, Br or I; PA1 M' is a metallating agent such as Li, Na, K, NaH, KH, or Li alkyl; PA1 M.sup.1 is a transition metal such as Sc, Ti, Zr, Hf, Fe, V or Cr; PA1 X.sup.1 is Cl, Br or I; PA1 m is the oxidation state of M.sup.1 ; and PA1 n.ltoreq.m. PA1 M.sup.1 is a transition metal such as Sc, Ti, Zr, Fe, V or Cr; PA1 X.sup.1 is Cl, Br or I; PA1 m is the oxidation state of M.sup.1 ; and PA1 n.ltoreq.is m;
A disadvantage of this procedure was that after the reaction of 3-alkylcyclopenten-1-ones with Grignard compounds or lithium alkyls, the resulting alkoxide (2) first had to be hydrolyzed by means of water and isolated as alcohol (3) before, upon separate catalytic dehydration and work-up, the desired 1,3-dialkylcyclopentadiene component (4) was then obtained, and compound (3) could only be used for the further reaction after separate drying (Tetrahedron 1965, 21, 2313; Chem. Ber. 1976, 109, 329; J. Organomet. Chem., 1991, 417, 9).
It was therefore an object of the invention to simplify the reactions I., II. and III. (equation (1)) to such a degree as to provide a process which allows, in one reaction without isolation of the intermediates, the synthesis in high yields of 1,3-disubstituted cyclopentadienes which can then be reacted to give the corresponding transition metal complexes, e.g. according to equation (2): ##STR2## wherein Cp denotes cyclopentadienyl;